In conventional grille systems, airflow through the grille assembly to motor vehicle components is substantially unimpeded. Advantageously, particularly at highway speeds this provides a source of cooling air to vehicle components such as the motor, radiator, etc. However, when the vehicle engine and cooling system are not operating at high capacity and so require less additional cooling, such unimpeded airflow is unnecessary. Moreover, such airflow is known to increase aerodynamic drag of the vehicle, lessening fuel economy.
For that reason, it is known to provide grille shutter systems for motor vehicles to lessen aerodynamic drag and so improve fuel economy. Such grille shutter systems include a series of vanes which may be opened or closed to increase or decrease airflow as needed. When increased airflow is required such as for cooling purposes, the vanes may be partially or fully opened to increase airflow through the vehicle radiator and into the engine compartment. When less airflow is required, for example when the motor and/or radiator are not operating at a high capacity and so requires less cooling, the vanes may be partially or fully closed to lessen airflow into the engine compartment. When the grille shutter system is closed, aerodynamic drag is reduced, improving aerodynamic properties of the vehicle and so improving fuel economy. A further advantage is that a vehicle operating with a closed grille shutter system requires less warm-up time in cold weather. As one example, active grille shutter systems are known in the art, which include vanes that open and close automatically to control airflow as needed.
It is likewise known to provide a front bumper step in a variety of motor vehicles, particularly tall vehicles such as trucks. The front bumper step provides convenience to the vehicle user, for example when there is a need to access the interior of the engine compartment.
Industry standards require a 15 mm to 21 mm design gap between a frame-mounted bumper and other elements of the vehicle body, such as the vehicle radiator frame-mount/radiator grille. However, particularly in vehicles equipped with front grille shutter systems, it has been found that even when the grille shutter system is in the closed configuration, this design gap provides an airflow leak that can increase aerodynamic drag and concomitantly decrease fuel economy, due to the redirection of airflow through the gap. Accordingly, a need in the art exists for designs which eliminate this increased drag in vehicles with grille shutter systems.